Friday, January 12, 2007

How Many Users Does It Take...?

No, that's not the set up to a bad joke. It's a legitimate question many people ask when developing and administering a usability test.

When I speak with people on this subject, I often refer to an article written by Jakob Nielsen called Usability Testing With 5 Users. It's not necessary to get 20 or 30 users to test an application when 5 will actually do the job. Statistically, 5 users will do and he explains how in his article.

I sometimes feel this is what scares most developers away from conducting objective, valid usability tests. Recruiting 20 to 30 users can be quite an undertaking. Administering a usability test with as many users can be even more difficult if time is of the essence. Instead, they rest their faith in the application and hope that their up front analysis (user research and task analysis) covered what was needed to build a usable application. Often, this is not the case.

In a future blog post I will be expanding on this subject by discussing personas in the development of usability case studies or scenarios. If the application being developed is complex and has many different users who use the same application in many different ways, a usability test following experimental rigor needs to be developed.

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